Radon Mitigation Options: SSD, SMD, and Passive Systems
Radon mitigation options for residential homes fall into four primary categories: sub-slab depressurization (SSD), sub-membrane depressurization (SMD) for crawlspaces, passive stack ventilation, and active soil depressurization variants for specific foundation conditions. Each method exists for a specific foundation type and concentration range, and choosing the right method depends on the home’s construction, the measured radon level, and the cost-benefit math of installation. This guide covers each method, when it is appropriate, what the system looks like, and typical Front Range pricing. EPA Radon Mitigation Standards (EPA 402-R-13-001) define the technical performance criteria, and NRPP/NRSB certify the professionals who install systems. Material here summarizes EPA, CDPHE, ANSI/AARST, and Lung Association guidance current as of 2026.
The four primary mitigation options
Sub-slab depressurization (SSD), sub-membrane depressurization (SMD), passive stack ventilation, and active soil depressurization (ASD) variants cover roughly 95% of residential radon mitigation in the United States. Each works by creating a pressure differential that draws radon out of the soil before it enters the home. SSD does this through a vent pipe penetrating the slab; SMD does it under a sealed plastic membrane in a crawlspace; passive systems rely on stack effect alone; and ASD variants extend SSD logic to specific foundation conditions like drain tile loops or block walls.
Other methods exist but are less commonly applied: heat-recovery ventilator (HRV) dilution, sealing-only approaches, and pressurization of the home interior. EPA does not recommend these as standalone solutions because they rarely achieve the 80% to 99% reduction that SSD and SMD systems routinely produce. The radon testing pillar guide for Front Range homeowners covers the measurement step that precedes any mitigation decision. EPA Radon Mitigation Standards set the performance criteria, and the radon venting system SSD explainer walks through how the soil-gas exhaust mechanism actually works in a typical installation.
Option 1: Sub-slab depressurization (SSD)
SSD is the most common residential radon mitigation method and the recommended first choice for any home with a concrete slab foundation (basement or slab-on-grade). The system consists of a vent pipe drilled through the slab into the soil or aggregate beneath, connected to an in-line fan that draws air out of the sub-slab area and exhausts it above the roof line. The continuous suction creates a low-pressure zone under the slab that prevents radon from migrating up through cracks and penetrations into the living space.
A properly designed SSD system reduces indoor radon concentrations by 80% to 99%. The system runs continuously and uses about $50 to $150 per year in electricity. The fan is rated for 5 to 10 years of service life and is the only routine replacement item. Front Range installation typically runs $1,500 to $3,500 depending on home size, slab condition, and how easily the vent stack can be routed.
SSD design details that matter
The vent pipe size (3-inch or 4-inch PVC), fan selection (radon-rated in-line fan), suction pit dimensions, and exhaust termination height (above the roof, away from windows and HVAC intakes) all affect performance. ANSI/AARST and EPA standards specify minimum requirements for each element. A defensible SSD installation includes a U-tube manometer or warning device that confirms the fan is operating continuously, audible warning if pressure drops, and labeled access points for future service.
Option 2: Sub-membrane depressurization (SMD)
SMD is the SSD equivalent for crawlspace foundations. Crawlspaces typically have exposed dirt or stone floors rather than concrete slabs, so the depressurization point is a sealed plastic membrane (typically 6-mil or thicker reinforced polyethylene) laid over the soil, with edges sealed to foundation walls and seams overlapped and taped. A vent pipe penetrates the membrane, connects to an in-line fan, and exhausts above the roof line.
SMD performance depends heavily on membrane integrity. Tears, gaps at wall seals, or missing seam tape compromise the pressure differential and reduce system effectiveness. Proper crawlspace preparation — removing debris, leveling the soil surface, ensuring access for future inspection — is critical to a successful installation. Front Range SMD installations run $2,500 to $4,500, somewhat higher than SSD because of the membrane installation labor.
Option 3: Passive stack ventilation
Passive systems use the stack effect (warm indoor air rising) to draw soil gas up through a vent pipe without an active fan. The pipe runs from a sealed sub-slab or sub-membrane area straight up through the building to terminate above the roof. Warm air in the pipe rises and pulls additional air from below, creating a passive depressurization effect.
Passive systems work in homes with strong stack effect (tall vent runs, significant indoor-outdoor temperature differentials, low baseline radon concentrations). They are most often installed as part of radon-resistant new construction (RRNC) features in new homes built in EPA Zone 1 counties. Performance is typically modest — 30% to 60% reduction — and passive systems often need to be upgraded to active fans if post-construction testing shows continued elevated levels. The upgrade cost (fan retrofit) is $400 to $900 if the vent stack is already in place.
Option 4: Active soil depressurization variants
Several variants of SSD address specific foundation conditions. Drain tile depressurization connects to an existing perimeter drain tile loop and applies suction at that point, useful for homes with drain tile in good condition and accessible loops. Block wall depressurization treats hollow-block foundation walls as the depressurization point, drawing air from the cavities in the blocks. Submembrane variants combine SMD and SSD for mixed-foundation homes (partial basement with crawlspace).
Each variant is appropriate for specific construction conditions and is more expensive than standard SSD because of the additional design complexity. Drain tile depressurization typically runs $2,000 to $4,000. Block wall depressurization runs $2,500 to $5,000. These options are not first-line solutions for typical slab construction.
Why fan selection determines system longevity
The in-line fan is the most critical component in any active mitigation system and the only component with a routine replacement schedule. Radon-specific fans (RadonAway RP series, Festa Radon, AMG, and similar manufacturers) are designed for continuous duty, sealed bearings, and weather-resistant outdoor installation. The fan motor runs 8,760 hours per year (every hour of every day), accumulating service hours faster than nearly any other household appliance.
Fan replacement intervals run 5 to 10 years depending on quality and operating conditions. Cheap fans from generic suppliers may fail within 2 to 4 years; premium fans from specialist suppliers typically deliver 8 to 12 years. The cost differential at installation is small ($100 to $200), and homeowners benefit from specifying the fan brand and model at the quote stage. Replacement fans run $200 to $500 plus labor.
How exhaust termination affects system performance and code compliance
The vent stack must terminate above the roof line, away from windows and HVAC intakes, with a downward-facing discharge to prevent rain entry. ANSI/AARST and EPA standards specify minimum distances: 10 feet horizontal from any opening, 2 feet above any opening within 10 feet, and routed so the discharge does not impinge on adjacent properties. Improper exhaust termination is a common installation defect and can cause radon to re-enter the home through nearby openings.
The vent pipe is typically 3-inch or 4-inch Schedule 40 PVC, supported with appropriate clamps and brackets, and insulated in unconditioned spaces to prevent condensation. Exterior vent pipe runs are typically along an outside wall, terminated above the roof eave. Interior vent pipe runs through attic spaces and out a roof penetration are also common. Local building codes may require specific routing or termination details, and the mitigation professional should obtain any required permits.
How to choose the right mitigation option
The choice depends on three factors: foundation type, measured radon concentration, and home size. For a concrete-slab foundation with measured levels of 4 to 20 pCi/L, SSD is the default first choice. For a crawlspace foundation with the same concentration range, SMD is the default. For very high concentrations (above 20 pCi/L) or unusual construction (mixed foundations, block walls, large home), a NRPP- or NRSB-certified mitigation professional should perform a diagnostic visit to recommend the appropriate variant.
Multi-fan systems are sometimes needed for large or complex homes. A single SSD fan can effectively depressurize roughly 1,500 to 2,500 square feet of slab area. Larger homes or homes with multiple slab levels may need two or three fans on separate vent pipes. The mitigation professional designs the system based on a diagnostic walk-through and any communication tests under the slab.
What homeowners pay for
Front Range pricing in 2026 for the four primary options: SSD on a typical 1,500 to 2,500 sq ft home runs $1,500 to $3,500 installed. SMD on a crawlspace runs $2,500 to $4,500. Passive stack ventilation as an RRNC feature in new construction runs $500 to $1,000 (cost is bundled into construction; rarely a standalone homeowner purchase). Drain tile or block wall variants run $2,000 to $5,000. Pricing includes design, materials, installation labor, electrical hookup, and post-installation diagnostic testing.
Post-mitigation testing
Every mitigation installation should be followed by post-installation testing to verify performance. EPA recommends a short-term (48-hour to 7-day) test placed in the same location as the pre-mitigation measurement. The post-mitigation result confirms the system is achieving the design reduction. If the post-test exceeds 4 pCi/L, the mitigation professional returns to diagnose and adjust the system at no additional cost (this should be a contract term).
EPA also recommends long-term re-testing every two years after mitigation to confirm continued performance. Fan failures, vent pipe blockages, or membrane damage can compromise a system silently if no one is monitoring. Re-testing is inexpensive (free test kits from CDPHE; $25 to $50 for hardware-store kits) and provides ongoing assurance.
What HRV and ERV ventilation does and does not do for radon
Heat recovery ventilators (HRV) and energy recovery ventilators (ERV) provide whole-house mechanical ventilation by exchanging indoor air with outdoor air through a heat-exchanging core. They can reduce indoor radon concentrations by dilution — bringing in low-radon outdoor air to replace high-radon indoor air. The reduction is typically 25 to 50%, well below the 80 to 99% achievable with SSD or SMD.
HRV/ERV is appropriate as a supplemental approach for homes that need both improved indoor air quality (humidity control, VOC reduction, CO2 reduction) and modest radon reduction. It is not appropriate as the primary mitigation for homes with significantly elevated radon. Cost runs $3,000 to $6,000 for a whole-house HRV/ERV system, comparable to a high-end SSD installation but with lower radon reduction. The right system choice depends on the homeowner’s broader indoor air quality goals.
When to call a professional
Radon mitigation is professional work. NRPP-certified or NRSB-certified mitigation professionals are trained in EPA Radon Mitigation Standards and ANSI/AARST design criteria. CDPHE maintains the Colorado certified-mitigator roster. Verify credentials before hiring, get two or three quotes, confirm post-installation testing is included, and require a warranty on the fan and labor. Avoid firms that bundle measurement and mitigation under one roof — independent measurement first, then competitive mitigation quotes.
References
- EPA Consumer’s Guide to Radon Reduction — Environmental Protection Agency
- CDPHE Colorado radon mitigation contractor roster — Colorado Department of Public Health and Environment
- InterNACHI radon mitigation installation overview — International Association of Certified Home Inspectors
- American Lung Association radon mitigation guidance — American Lung Association
Front Range homeowners who tested above 4 pCi/L can reach out through our contact page for a referral to a NRPP-certified mitigation professional who installs SSD and SMD systems across the Denver metro corridor.